Generally, in tomographic imaging methods inner structures of an examination object can be examined without operations having to be performed on the object. One possible type of tomographic image generation consists in recording a number of projections of the object to be examined from different angles. A two-dimensional sectional image or a three-dimensional volume image of the examination object can be calculated from these projections.
One example of a tomographic imaging method is computed tomography. Methods for scanning an examination object using a CT system are generally known. For example, circular scannings, sequential circular scannings with feed or spiral scannings are used. Other types of scannings, which are not based on circular movements, are also possible (e.g., scans with linear segments). Absorption data of the examination object is recorded from different recording angles with the aid of at least one x-ray source and at least one opposite detector and this thus collected absorption data and/or these projections are allocated to sectional images through the examination object by way of corresponding reconstruction methods.
A so-called Filtered Back Projection (FBP) is typically used as the standard method for reconstructing computed tomography images from x-ray CT data records of a computed tomography device (CT device), i.e. from the captured projections. A so-called “rebinning” step is usually carried out after the data acquisition, in which step the data generated with the beam which propagates from the source in a fan-type fashion is rearranged such that it exists in a form as if the detector was hit by x-ray beams heading in parallel for the detector. The data is then transformed into the frequency range. A filtering takes place in the frequency range, and the filtered data is then transformed back. A back projection onto the individual voxels within the volume of interest then takes place with the aid of the thus rearranged and filtered data.
During the acquisition of the CT measurement data, the examination object, generally a patient, is exposed to a dose of x-ray radiation. Because this radiation is generally not harmless to the examination object, attempts are made to manage with as low a radiation exposure as possible. The dose used is nevertheless directly connected to the image noise in the image data reconstructed from the CT measurement data. A reduction in the dose results in an increase in the noise. In order to utilize as effectively as possible a specific radiation dose, it is therefore desirable to use image reconstruction or image processing methods which efficiently reduce the noise in CT images.